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{ “title”: “Use Workload Group limit local IO”, “language”: “en” }

In OLAP systems, when performing ETL or large ad-hoc queries, a significant amount of data needs to be read. To speed up data analysis, Doris internally uses multithreading to scan multiple disk files in parallel, which generates a large amount of disk I/O and can negatively impact other queries, such as report analysis.

By using Workload Groups, you can group offline ETL data processing and online report queries separately and limit the I/O bandwidth for offline data processing, thereby reducing its impact on online report analysis.

Test limit local IO

Test

1FE,1BE(96 cores), test data is clickbench

Not limit IO

1. Clear cache.

// clear OS cache.
sync; echo 3 > /proc/sys/vm/drop_caches

// disable BE's cache.
disable_storage_page_cache = true

2. Run query one by one.

set dry_run_query = true;
select * from hits.hits;

3. Show local IO by system table, is's 3G/s.

mysql [information_schema]>select LOCAL_SCAN_BYTES_PER_SECOND / 1024 / 1024 as mb_per_sec from workload_group_resource_usage where WORKLOAD_GROUP_ID=11201;
+--------------------+
| mb_per_sec         |
+--------------------+
| 1146.6208400726318 |
+--------------------+
1 row in set (0.03 sec)

mysql [information_schema]>select LOCAL_SCAN_BYTES_PER_SECOND / 1024 / 1024 as mb_per_sec from workload_group_resource_usage where WORKLOAD_GROUP_ID=11201;
+--------------------+
| mb_per_sec         |
+--------------------+
| 3496.2762966156006 |
+--------------------+
1 row in set (0.04 sec)

mysql [information_schema]>select LOCAL_SCAN_BYTES_PER_SECOND / 1024 / 1024 as mb_per_sec from workload_group_resource_usage where WORKLOAD_GROUP_ID=11201;
+--------------------+
| mb_per_sec         |
+--------------------+
| 2192.7690029144287 |
+--------------------+
1 row in set (0.02 sec)

4.Show IO by pidstat, the first column in picture is process id, the second column is IO(kb/s), it's 2G/s.

Test IO limit.

1. Clear cache.

// clear os cache
sync; echo 3 > /proc/sys/vm/drop_caches

// disable BE cache
disable_storage_page_cache = true

2. Alter workload group.

alter workload group g2 properties('read_bytes_per_second'='104857600');

3. Show IO by system table, it's about 98M/s.

mysql [information_schema]>select LOCAL_SCAN_BYTES_PER_SECOND / 1024 / 1024 as mb_per_sec from workload_group_resource_usage where WORKLOAD_GROUP_ID=11201;
+--------------------+
| mb_per_sec         |
+--------------------+
| 97.94296646118164  |
+--------------------+
1 row in set (0.03 sec)

mysql [information_schema]>select LOCAL_SCAN_BYTES_PER_SECOND / 1024 / 1024 as mb_per_sec from workload_group_resource_usage where WORKLOAD_GROUP_ID=11201;
+--------------------+
| mb_per_sec         |
+--------------------+
| 98.37584781646729  |
+--------------------+
1 row in set (0.04 sec)

mysql [information_schema]>select LOCAL_SCAN_BYTES_PER_SECOND / 1024 / 1024 as mb_per_sec from workload_group_resource_usage where WORKLOAD_GROUP_ID=11201;
+--------------------+
| mb_per_sec         |
+--------------------+
| 98.06641292572021  |
+--------------------+
1 row in set (0.02 sec)

4. Show IO by pidstat, the process IO is about 131M/s。

NOTE

1. The LOCAL_SCAN_BYTES_PER_SECOND field in the system table represents the aggregated statistics at the process level for the current Workload Group. For example, if 12 file paths are configured, LOCAL_SCAN_BYTES_PER_SECOND represents the maximum I/O value across these 12 file paths. If you want to see the I/O throughput for each file path individually, you can view detailed values in Grafana or through the BE's bvar monitoring.
2. Due to the presence of the operating system‘s and Doris’s Page Cache, the I/O values observed using Linux's I/O monitoring scripts are usually smaller than those seen in the system table.